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Yes. If you are getting that result then it is not reading the PROM chip and the first thing to do is check your soldering work. You'll most likely find a pin that has not soldered to the board properly even if they all "look" like they are.

I check for low resistance between PROM socket pins with a multimeter.
Apart from a couple of pins that a re 30-40k ohm the rest are in the megs. I have found the a couple with low resistance between the pins that clear by heating the affected pin and allowing the solder to flow.
I have had a non booting board that was caused by a solder splatter away from the PROM. A brush with a bristle paintbrush (not nylon) with the board upside down should clear these as they usually aren't well stuck on.

Providing you are getting +12V from the power supply on the yellow/black wires and +5V from the red/black wires (or thereabouts it does not have to be dead on accurate) then you are most likely still having a failure to read the PROM.

I've created a document that traces out every pin from the PROM to the nearest top solder point to help people ensure that they have continuity if that helps:

I checked the continuity based on the document and everything checked out. I couldn't check pins 24 and 31 as they go to via holes on the PCB. I tried scraping some of the resist off above the via hole but was worried I'd inadvertently cut through a track.

I also checked adjacent pins for short circuits and didn't find any.

My next guess is the PROM failed, but I've worked on another product in the past which uses the same PROM and I don't recall any failing.

Rare for it to be the PROM. I'll say you have either a fine blob of solder or debris somewhere or (also rare) something else has failed. From here if there is nothing visually obvious it may need some more advanced assistance.